Temperature management of catalyst system for a variable displacement engine

ABSTRACT

A system and method for controlling an internal combustion engine having a plurality of cylinders, at least some of which may be selectively deactivated to provide variable displacement operation, include managing temperature of at least one engine/vehicle component by monitoring the temperature of the component and controlling activation of at least one cylinder to control the temperature of the component. In one embodiment, the engine/vehicle component is an emission control device, such as a catalytic converter.

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application is a continuation of co-pending and commonlyowned U.S. patent application Ser. No. 09/732,262, filed Dec. 7, 2000,now U.S. Pat. No. 6,______, the disclosure of which is incorporated byreference in its entirety.

BACKGROUND OF INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to a system and method forcontrolling a variable displacement engine to manage temperature of acatalyst system.

[0004] 2. Background Art

[0005] Fuel economy for a multi-cylinder internal combustion engine canbe improved by deactivating some of the engine cylinders under certainoperating conditions. Reducing the number of operating cylinders reducesthe effective displacement of the engine such that it is sometimesreferred to as a variable displacement engine. Depending upon theparticular configuration of the variable displacement engine, one ormore cylinders may be selectively deactivated to improve fuel economyunder light load conditions. In some configurations, a group ofcylinders, which may be an entire bank of cylinders, is selectivelydeactivated.

[0006] Reducing the number of operating cylinders may also reduce theoperating temperature of various engine and/or vehicle components whichmay adversely affect desired engine operation. For example, certainemission control devices, such as catalytic converters, require aminimum operating temperature for efficient operation. One approach toraise catalyst temperature involves enriching the fuel supply to theoperating cylinders when catalyst temperature drops below a specifiedlevel as disclosed in U.S. Pat. No. 4,467,602. This method assumes thatexcess air is available in the catalytic converter to be effective. Theinventors herein have recognized that this assumption may not always bevalid and may result in reduced catalyst and/or engine efficiency duringcertain operating conditions.

SUMMARY OF INVENTION

[0007] An object of the present invention is to provide a system andmethod for controlling a variable displacement internal combustionengine to effectively manage the temperature of one or more engineand/or vehicle components.

[0008] In carrying out the above object and other objects, advantagesand features of the invention, a system and method for controlling avariable displacement internal combustion engine include controlling thenumber or ratio of active/inactive cylinders to control the temperatureof at least one engine or vehicle component. In one preferredembodiment, the system and method include controlling a variabledisplacement engine having a bank configuration with a close-coupledcatalyst associated with each bank of cylinders and at least onedownstream or underbody catalyst by activating the second bank ofcylinders when one of the catalysts is determined to be near or below aminimum efficient operating temperature.

[0009] The present invention provides a number of advantages. Forexample, the present invention manages the temperature of one or moreengine/vehicle components to maintain a desired operating efficiencywhile also efficiently operating the engine.

[0010] The above advantage and other advantages, objects and features ofthe present invention will be readily apparent from the followingdetailed description of the preferred embodiments when taken inconnection with the accompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

[0011]FIG. 1 is a block diagram illustrating operation of one embodimentfor a system or method for controlling a variable displacement engineaccording to the present invention;

[0012]FIG. 2 is a block diagram illustrating operation of anotherembodiment for a system or method for controlling a variabledisplacement engine according to the present invention;

[0013]FIG. 3 is a logic diagram illustrating a reactivation strategy forcylinders of a variable displacement engine to manage componenttemperature according to one embodiment of the present invention; and

[0014]FIG. 4 is a flow diagram illustrating operation of one embodimentfor a system or method for controlling a variable displacement engineaccording to the present invention.

DETAILED DESCRIPTION

[0015] A block diagram illustrating an engine control system for arepresentative internal combustion engine operable in a variabledisplacement mode to manage temperature of an engine/vehicle componentaccording to the present invention is shown in FIG. 1. System 10preferably includes an internal combustion engine 12 having a pluralityof cylinders, represented by cylinder 14. In one preferred embodiment,engine 12 includes ten cylinders arranged in a “V” configuration havingtwo cylinder banks with five cylinders each. As used herein, a cylinderbank refers to a related group of cylinders having a commoncharacteristic, such as being located proximate one another, having acommon emission control device (ECD), or related according to firingorder, for example. As such, cylinder banks can also be defined forin-line cylinder configurations as well.

[0016] As one of ordinary skill in the art will appreciate, system 10includes various sensors and actuators to effect control of the engine.One or more sensors or actuators may be provided for each cylinder 14,or a single sensor or actuator may be provided for the engine. Forexample, each cylinder 14 may include four actuators which operatecorresponding intake and exhaust valves, while only including a singleengine coolant temperature sensor.

[0017] System 10 preferably includes a controller 16 having amicroprocessor 18 in communication with various computer-readablestorage media, indicated generally by reference numeral 20. The computerreadable storage media preferably include a read-only memory (ROM) 22, arandom-access memory (RAM) 24, and a keep-alive memory (KAM) 26. Asknown by those of ordinary skill in the art, KAM 26 is used to storevarious operating variables while controller 16 is powered down but isconnected to the vehicle battery. Computer-readable storage media 20 maybe implemented using any of a number of known memory devices such asPROMs, EPROMs, EEPROMs, flash memory, or any other electric, magnetic,optical, or combination memory device capable of storing data, some ofwhich represents executable instructions, used by microprocessor 18 incontrolling the engine. Microprocessor 18 communicates with the varioussensors and actuators via an input/output (I/O) interface 32. Of course,the present invention could utilize more than one physical controller,such as controller 16, to provide engine/vehicle control depending uponthe particular application.

[0018] In operation, air passes through intake 34 where it may bedistributed to the plurality of cylinders via an intake manifold,indicated generally by reference numeral 36. System 10 preferablyincludes a mass airflow sensor 38 which provides a corresponding signal(MAF) to controller 16 indicative of the mass airflow. If no massairflow sensor is present, a mass airflow value may be inferred fromvarious engine operating parameters. A throttle valve 40 may be used tomodulate the airflow through intake 34 during certain operating modes.Throttle valve 40 is preferably electronically controlled by anappropriate actuator 42 based on a corresponding throttle positionsignal generated by controller 16. A throttle position sensor provides afeedback signal (TP) indicative of the actual position of throttle valve40 to controller 16 to implement closed-loop control of throttle valve40.

[0019] As illustrated in FIG. 1, a manifold absolute pressure sensor 46may be used to provide a signal (MAP) indicative of the manifoldpressure to controller 16. Air passing through intake 34 enters thecombustion chambers or cylinders 14 through appropriate control of oneor more intake valves. The intake and exhaust valves may be controlleddirectly or indirectly by controller 16 along with ignition timing(spark) and fuel to selectively activate/deactivate one or morecylinders 12 to provide variable displacement operation. A fuel injector48 injects an appropriate quantity of fuel in one or more injectionevents for the current operating mode based on a signal (FPW) generatedby controller 16 processed by an appropriate driver. Control of the fuelinjection events is generally based on the position of the pistonswithin respective cylinders 14. Position information is acquired by anappropriate crankshaft sensor which provides a position signal (PIP)indicative of crankshaft rotational position. At the appropriate timeduring the combustion cycle, controller 16 generates a spark signal (SA)which is processed by ignition system 58 to control spark plug 60 andinitiate combustion within an associated cylinder 14.

[0020] Controller 16 (or a camshaft arrangement) controls one or moreexhaust valves to exhaust the combusted air/fuel mixture of activated orrunning cylinders through an associated exhaust manifold, indicatedgenerally by reference numeral 28. Depending upon the particular engineconfiguration, one or more exhaust manifolds may be used. In onepreferred embodiment, engine 12 includes an exhaust manifold 28associated with each bank of cylinders as illustrated in FIG. 1.

[0021] An exhaust gas oxygen sensor 62 is preferably associated witheach bank of cylinders and provides a signal (EGO) indicative of theoxygen content of the exhaust gases to controller 16. The presentinvention is independent of the particular type of exhaust gas oxygensensor utilized, which may depend on the particular application. In oneembodiment, heated exhaust gas oxygen sensors (HEGO) are used. Ofcourse, various other types of air/fuel ratio sensors/indicators may beused such as a universal exhaust gas oxygen sensor (UEGO), for example.The exhaust gas oxygen sensor signals may be used to independentlyadjust the air/fuel ratio, or control the operating mode of one or morecylinders or banks of cylinders. The exhaust gas passes through theexhaust manifolds 28 through associated upstream emission controldevices 64A and 64B which may be catalytic converters, for example.After passing through the associated upstream ECDs, the exhaust gas iscombined and flows past an underbody exhaust gas oxygen sensor 66 andthrough a downstream emission control device 68 before flowing past acatalyst monitoring sensor 70 (typically another exhaust gas oxygensensor) and being exhausted to atmosphere.

[0022] A temperature sensor 72 may be provided to monitor thetemperature of a catalyst within emission control device 68, dependingupon the particular application. Alternatively, the temperature may beestimated using an appropriate temperature model based on various othersensed engine/vehicle parameters which may include mass airflow,manifold absolute pressure or load, engine speed, air temperature,engine coolant temperature, and/or engine oil temperature, for example.A representative temperature model could be developed to determinecatalyst temperature for any one of the emission control devices 64A,64B and/or 68 using various sensed and estimated engine operatingparameters as described in U.S. Pat. No. 5,956,941, for example.

[0023] According to the present invention, controller 16 managestemperature of one or more engine/vehicle components, such as emissioncontrol devices 64A, 64B, and/or 68 by controllingactivation/deactivation of one or more cylinders. In a preferredembodiment, engine 12 is a V-10 engine with variable displacementoperation provided by selectively deactivating one bank of cylindersunder appropriate engine and/or vehicle operating conditions, such aslight load, for example. The deactivated cylinder bank may then beselectively activated to maintain efficient operation of one or moreemission control devices. For example, the second cylinder bank may bereactivated to maintain the temperature of emission control device 68sufficiently above the catalyst light-off temperature to maintainefficient operation. The cylinder bank is then deactivated after thetemperature exceeds a corresponding threshold to provide hysteresis, orto reduce the operating temperature to prolong component life, forexample, as explained in greater detail below.

[0024] Referring now to FIG. 2, an alternative embodiment forcontrolling a variable displacement engine to manage temperature of anengine/vehicle component according to the present invention is shown. Aswill be recognized by those of ordinary skill in the art, system 100includes similar components as described with reference to theembodiment illustrated in FIG. 1 and incorporated here by reference.Internal combustion engine 102 includes two cylinder banks 104, 106.Each cylinder bank includes an associated upstream or close-coupledemission control device 108 and 110, respectively. In addition, ratherthan combining the exhaust and using a common third emission controldevice as illustrated in FIG. 1, each bank 104, 106 also has anassociated downstream or underbody emission control device 112, 114,respectively. In one embodiment, the emission control devices 108, 110,112, and 114 are three-way catalysts.

[0025] As also illustrated in FIG. 2, each ECD has an associated exhaustgas oxygen sensor 116, 118, 120, 122, respectively, which are preferablyHEGO sensors. Additional exhaust gas oxygen sensors 124, 126 may beprovided downstream relative to downstream ECDs 112, 114, respectively,to provide a conversion efficiency indication and monitor operation ofthe emission control devices. Downstream ECDs 112, 114 preferablyinclude associated temperature sensors 128, 130 to provide an indicationof the catalyst temperature which may be used by controller 132 tomanage the temperature of one or more of the ECDs as described herein.It should be recognized by those of ordinary skill in the art that thetemperature of one or more engine/vehicle components can be modeled asdescribed above with reference to the embodiment illustrated in FIG. 1.Component temperature modeling may be used alone or in combination withone or more temperature sensors to provide temperature managementaccording to the present invention. One of ordinary skill in the artwill also recognize that a variety of engine/vehicle operatingparameters influence the current operating mode and selectiveactivation/deactivation of one or more cylinders to provide variabledisplacement operation. These parameters may affect or override thedecision to activate/deactivate cylinders to provide the temperaturemanagement features in accordance with the present invention.

[0026] The diagrams of FIGS. 3 and 4 generally represent control logicfor one embodiment of a system or method according to the presentinvention. As will be appreciated by one of ordinary skill in the art,the diagrams may represent any one or more of a number of knownprocessing strategies such as event-driven, interrupt-driven,multi-tasking, multi-threading, and the like. As such, various steps orfunctions illustrated may be performed in the sequence illustrated, inparallel, or in some cases omitted. Likewise, the order of processing isnot necessarily required to achieve the objects, features, andadvantages of the invention, but is provided for ease of illustrationand description. Although not explicitly illustrated, one of ordinaryskill in the art will recognize that one or more of the illustratedsteps or functions may be repeatedly performed depending upon theparticular processing strategy being used.

[0027] Preferably, the control logic is implemented primarily insoftware executed by a microprocessor-based engine controller. Ofcourse, the control logic may be implemented in software, hardware, or acombination of software and hardware depending upon the particularapplication. When implemented in software, the control logic ispreferably provided in a computer-readable storage medium having storeddata representing instructions executed by a computer to control theengine. The computer-readable storage medium or media may be any of anumber of known physical devices which utilize electric, magnetic,and/or optical devices to temporarily or persistently store executableinstructions and associated calibration information, operatingvariables, and the like.

[0028] Block 150 of FIG. 3 represents monitoring of at least one engineor vehicle component such as an emission control device (END). In thisembodiment, block 150 determines whether an upstream ECD is above acorresponding or associated temperature threshold. For example, thetemperature threshold may correspond to be light-off temperature of athree-way catalyst. Block 152 determines whether a downstream ECD isabove a corresponding temperature. The downstream ECD may be associatedwith a single upstream device, as illustrated in FIG. 2, or shared bymultiple upstream devices as illustrated in FIG. 1. If the upstream ECDis above the corresponding temperature threshold as determined by block150 and the downstream ECD is above its associated temperature thresholdas determined by block 152, all cylinders are operated under closed-loopcontrol with a normal scheduled air/fuel ratio and spark or ignitiontiming as represented by block 154.

[0029] If the upstream component is below its associated temperaturethreshold as indicated by block 150, or the downstream component isbelow its associated temperature threshold as indicated by block 152,block 156 determines whether an associated exhaust gas oxygen sensor isavailable in providing information sufficient to operate closed-loop. Inthis particular embodiment, block 156 determines whether an associatedHEGO sensor has reached an appropriate operating temperature to providereliable information with respect to the oxygen content of the exhaustgas. If the associated HEGO is ready for closed-loop operation asdetermined by block 156, the previously deactivated cylinders areactivated with a lean bias on the air/fuel ratio and spark retarded fromMBT. The previously running or activated cylinders are operated with arich bias air/fuel ratio. All cylinders are operated using closed-loopcontrol of air/fuel ratio based on the HEGO sensor reading withappropriate lean/rich bias as represented by block 158. In oneembodiment, an entire bank of cylinders is activated and operated with alean bias and retarded spark until the downstream ECD reaches itstemperature threshold as determined by block 152.

[0030] If the HECO sensor associated with the ECD is not ready forclosed-loop operation as determined by block 156, the engine iscontrolled to activate the deactivated cylinders and operate themopen-loop with a lean air/fuel ratio and spark retarded from MBT asrepresented by block 160. The previously activated or running cylindersare operated with a rich bias air/fuel ratio in closed-loop mode.

[0031]FIG. 4 provides an alternative representation of operation for asystem or method to manage temperature of an engine/vehicle componentaccording to the present invention. Block 180 represents monitoring ofat least one catalyst temperature using a temperature model asrepresented by block 182 and/or an associated temperature sensor asrepresented by block 184. The engine/vehicle component, in thisembodiment a catalyst, is monitored and managed by controllingactivation of at least one cylinder in a variable displacement operatingmode to control the temperature of the component. In this example, block186 compares the catalyst temperature to a low temperature threshold. Ifthe temperature is below the associated low temperature threshold, block192 activates one or more deactivated cylinders to raise the temperatureof the catalyst. Block 194 controls the air/fuel ratio and/or sparkusing open-loop, closed-loop, or a combination, to control the variouscylinders as described with reference to FIG. 3 above. In oneembodiment, block 192 activates an entire bank of deactivated cylinders.Preferably, control of the activated and deactivated cylinders iscoordinated during reactivation such that the combined exhaustapproaches a stoichiometric air/fuel ratio.

[0032] Block 188 of FIG. 4 represents comparing the catalyst temperatureto an associated high temperature threshold to trigger deactivation ofone or more cylinders as represented by block 190. The comparisonrepresented by block 188 may be used to provide appropriate hysteresisto avoid hunting or cycling of the deactivated cylinders. Alternatively,or in combination, a temperature threshold may be provided as one formof component protection to reduce or prevent premature reduction of thecatalyst conversion efficiency.

[0033] As such, the present invention manages the temperature of one ormore engine/vehicle components such as an emission control device tomaintain a desired operating efficiency while also efficiently operatingthe engine.

[0034] While the best mode for carrying out the invention has beendescribed in detail, those familiar with the art to which this inventionrelates will recognize various alternative designs and embodiments forpracticing the invention as defined by the following claims.

1. A method for controlling a variable displacement internal combustionengine having a plurality of cylinders, at least some of which areselectively deactivated in a variable displacement operating mode, themethod comprising: monitoring temperature of at least one engine orvehicle component; and operating the engine in the variable displacementmode to deactivate at least one cylinder associated with the at leastone engine or vehicle component to decrease the temperature of thecomponent.
 2. The method of claim 1 wherein the step of monitoringtemperature comprises estimating the temperature.
 3. The method of claim1 wherein the engine or vehicle component is an emission control device.4. The method of claim 3 wherein the engine or vehicle component is athree-way catalyst.
 5. The method of claim 1 further comprisingactivating deactivated cylinders to increase the temperature of thecatalyst.
 6. The method of claim 1 further comprising: activating atleast one of the deactivated cylinders and controlling air/fuel ratio tothe at least one cylinder during activation to provide a lean air/fuelratio; controlling air/fuel ratio for a corresponding number ofactivated cylinders during activation of the at least one cylinder toprovide a rich air/fuel ratio; and controlling air/fuel ratio for allcylinders to provide a stoichiometric air/fuel ratio after reactivationof the at least one cylinder.
 7. The method of claim 6 furthercomprising retarding ignition timing for the at least one cylinderduring activation.
 8. A method for controlling a variable displacementinternal combustion engine having cylinders grouped into two banks withassociated separate upstream emission control devices and at least athird downstream emission control device, at least one bank beingselectively activated and deactivated to provide variable displacement,the method comprising: determining temperature of at least one of theemission control devices; activating both cylinder banks when thetemperature is below a low temperature threshold; and deactivating oneof the cylinder banks when the temperature is above a high temperaturethreshold.
 9. The method of claim 8 wherein the third downstreamemission control device is a shared emission control device positioneddownstream of both upstream emission control devices and wherein thestep of determining comprises determining the temperature of the thirdemission control device.
 10. The method of claim 8 wherein the step ofdetermining comprises estimating the temperature using a temperaturemodel.
 11. The method of claim 8 wherein the emission control devicesare three-way catalysts.
 12. The method of claim 8 wherein the step ofactivating comprises controlling air/fuel ratio to operate one bank richand one bank lean.
 13. The method of claim 12 wherein the step ofactivating comprises controlling ignition timing for the lean bank byretarding ignition timing from MBT timing.
 14. A system for controllingan internal combustion engine having a plurality of cylinders, at leastsome of which are selectively deactivated in a variable displacementoperating mode, the system comprising: first and second upstreamemission control devices; at least a third emission control devicepositioned downstream relative to at least one of the first and secondupstream emission control devices; and an engine controller formonitoring temperature of at least one of the emission control devicesand controlling activation/deactivation of at least one cylinder tomanage temperature of the at least one emission control device.
 15. Thesystem of claim 14 wherein the engine controller monitors temperature ofthe at least one emission control device using a temperature model ofthe emission control device.
 16. The system of claim 14 wherein theemission control devices comprise three-way catalysts.
 17. A computerreadable storage medium having stored data representing instructionsexecutable by a computer to control a variable displacement internalcombustion engine having a plurality of cylinders, at least some ofwhich are selectively deactivated in a variable displacement mode, thecomputer readable storage medium comprising: instructions for monitoringtemperature of at least one engine or vehicle component; andinstructions for controlling activation of at least one cylinder tocontrol the temperature of the component.
 18. The computer readablestorage medium of claim 17 further comprising instructions for modelingthe temperature of the component.
 19. The computer readable storagemedium of claim 18 further comprising: instructions for retardingignition timing relative to MBT ignition timing for the at least onecylinder during activation.